it83xx: add reset cause of reset pin
it83xx: add reset cause of reset pin

If reset was caused by reset pin, we need this reset cause
for next sequence(recovery key).

Signed-off-by: Dino Li <dino.li@ite.com.tw>

BRANCH=none
BUG=none
TEST=To assert EC WRST pin and we will get the reset cause for
     both power-on and reset-pin.

Change-Id: I0361091680a148df07cbbb8f4e53635dbf48fdee
Reviewed-on: https://chromium-review.googlesource.com/371798
Commit-Ready: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Tested-by: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec